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Starting today, archaeologists will be prodding what lies beneath the surface of grit and grime coating the parking lot behind San Francisco's current Transbay Terminal.

As part of the $4 billion project to replace the current Transbay Terminal at Mission and Beale streets, archaeologists will literally break ground to conduct testing in the Caltrans parking lot behind the terminal, according to the Transbay Joint Powers Authority, which oversees the project.

To ensure the project will not impact potentially significant historic or prehistoric archaeological deposits, archaeologists will use a backhoe to explore areas of the lot.

The exploration work is expected to go through early August, and work will take place on weekdays from 7 a.m. to 3:30 p.m.

Despite the presence of excavation equipment on the site, the archaeological investigations are not expected to disturb surrounding businesses.

The two-phase Transbay Transit Center Project broke ground in December on a temporary terminal located between Beale and Main streets and Howard and Folsom streets that is scheduled to open Aug. 7.

Once the new center is complete, which transit officials said could be by 2018, the regional transit hub will house nine Bay Area transportation systems and act as a terminus for the $43 billion high-speed rail line that will link the region to the rest of the state.

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In addition to replacing the outdated existing terminal, the transit project will extend the Caltrain rail line into the city's Financial District and redevelop the surrounding area into a residential neighborhood with offices, parks and shops.